A ribbon microphone, which is one type of microphone, includes a pair of magnets forming a magnetic field and a pair of ribbon diaphragms configured to vibrate in response to acoustic waves. The pair of ribbon diaphragms are disposed in the magnetic field. When the pair of ribbon diaphragms receive the acoustic waves, the pair of ribbon diaphragms vibrate in the magnetic field and generate electrical signals corresponding to the acoustic waves.
The typical ribbon microphones have bidirectivity. Microphones for collection of musical sounds or amplification of sound preferably have unidirectivity.
Unidirectivity of ribbon microphones is established through addition of a bidirectional component and an omnidirectional component. The unidirectivity of a ribbon microphone is established with a built-in acoustic tube in the ribbon microphone. Ribbon diaphragms have a small mass and a low mechanical impedance compared to those of diaphragms of other types of microphones, such as a dynamic microphone. The acoustic tube should have a large length to vibrate the ribbon diaphragms at low frequencies. That is, a unidirectional ribbon microphone requires a long acoustic tube. Thus, a reduction in dimensions of the unidirectional ribbon microphone is difficult.
With respect to techniques for reducing dimensions of a unidirectional ribbon microphone, techniques have been proposed to include a unidirectivity converter in place of an acoustic tube (for example, refer to Japanese Unexamined Patent Application Publication No. 2015-5861).